The invention pertains to a lighting device, especially for motor vehicles, which is comprised of a light source for sending out a light beam and a lightguide of elongated shape made of a plastic, primarily transparent material for guiding the light beam, while a portion of the mantle of the lightguide forms the exit surface for emergence of the rays of light.
A lighting device formed by a light guide of elongated shape, in whose body is arranged a light source and whose mantle in a particular portion lets through light and thus forms an exit surface for emergence of the light rays, is known from document EP1775511. Opposite the exit surface is arranged a reflective surface of the mantle, which is provided with optical elements (prisms). One portion of the rays passing through the lightguide is reflected from the reflection side (of the optical elements) in the direction of the outlet side of the lightguide and emerges to the outside through the outlet side of the lightguide. A second portion of rays passes through the reflection side and out from the lightguide, impinges upon and is bounced back from a diffuse part arranged outside the lightguide, passes through the reflection side, again enters into the lightguide and then emerges through the outlet side from the lightguide and to the outside. The lighting device according to document EP1775511 is unsuitable especially on account of the air gap between the lightguide and the diffuse part, which results in Fresnel losses at the interface between the diffuse part and the lightguide. If moreover the diffuse part is metallized, the efficiency of the system is further reduced due to the limited reflectivity of the metallized surface. Another document, DE102007005779A1, specifies a lighting device with a lightguide of elongated shape, provided in one peripheral part with projections, which reflect the rays of the light beam passing through the lightguide in the direction toward the opposite peripheral part of the lightguide, through which the rays pass to the outside and are finally reflected by a reflector in the direction of the movement of the vehicle. The lightguides known thus far for motor vehicles thus emit a light image which emerges by the outlet side of the mantle of the lightguide as a result of reflection from the optical elements arranged primarily on the side of the lightguide opposite the outlet side. The contours of the optical elements are quite visible in the emerging light image and they form undesirable discontinuous spots or sections. While making the optical elements smaller somewhat reduces the discontinuities visible in the light image, it does so only in a certain narrow range of the angle of observation. The lighting devices of the same kind that are known thus far also have a complicated design and installation, especially because they are composed of many parts. Each part requires its own press molds. Finally, assemblages of lighting devices of multiple parts are disadvantageous because they have relatively large dimensions, which limits their use in a vehicle frame.